Hot melt adhesive systems have many applications in manufacturing and packaging. For example, thermoplastic hot melt adhesives are used for carton sealing, case sealing, tray forming, pallet stabilization, nonwoven applications including diaper manufacturing, and many other applications. Hot melt adhesives often come in the form of various solids or pieces (hereinafter referred to as “particulate(s)”). These hot melt adhesive particulates are melted into a liquid form by a melter, and the liquid hot melt adhesive is ultimately applied to an object such as a work piece, substrate or product by a dispensing device suitable to the application.
A supply of unmelted hot melt adhesive particulate must be maintained and delivered to the melter in order for the melter to produce the liquid hot melt adhesive used by the dispensing device. For example, it is known for a person to employ a scoop or bucket to retrieve hot melt adhesive particulate from a bulk supply, and to deliver those particulate to the melter. Typically, this involves filling a hopper or other container associated with the melter one scoop of hot melt adhesive particulate at a time. This requires the person to handle the hot melt adhesive particulate closely, which may be undesirable because hot melt adhesive dust may be stirred up during handling. In addition, transferring hot melt adhesive particulate in this manner is prone to waste caused by spillage.
To address these concerns with hand filling, the solid particulate adhesive material may be provided on demand by automated filling, depending on the specific design of the melter. Moreover, some melters are designed in such a manner that hand filling is not possible. In some of these systems, the adhesive pellets are designed to be transferred by pressurized air from a pneumatic pump of a fill system into the melter, whenever the melter requires additional material to heat and dispense. In this regard, the fill system ensures that the amount of adhesive material within the melter remains at sufficient levels during operation of the dispensing system. The fill system must be supplied reliably with additional adhesive particulate in order to meet the demands of the melter during operation.
One particular type of fill system is defined by a tote-based pneumatic fill system. The tote-based pneumatic fill system includes a trash can-like wheeled supply container (which may also be referred to as a tote) with an interior space having a size sufficient to hold enough adhesive material for multiple hours of operation of the dispensing system. An adhesive bin defined by the tote may contain adhesive particulate for storage prior to melting in the adhesive melter. A transfer pump, such as a pneumatic pump, connects to the adhesive bin for moving the adhesive particulate via a hose from the adhesive bin to the adhesive melter. Pneumatic pumps generally rely on the suction of gas, such as air, entrained within gaps between individual pieces of adhesive particulate stored within the adhesive bin for moving the adhesive particulate. This gas may also be referred to as “make-up” gas.
Traditionally, the adhesive particulate gravity feeds into a lower portion of the adhesive bin toward an inlet of the transfer pump and submerges a majority of the pump inlet. The transfer pump generates a vacuum at the inlet that withdraws the entrained make-up gas and adhesive particulate therein. In turn, the suction of the entrained make-up gas creates a vacuum within the gaps of the adhesive particulate that withdraws additional gas from a surrounding environment. This additional gas must be drawn through the entire height of adhesive particulate stacked on top of the transfer pump inlet, which can be difficult. Thus, the transfer pumps in conventional tote-based fill systems may become starved for air to produce the vacuum required in order to continue moving adhesive particulate out of the adhesive bin.
Conventional tote-based systems also typically include a vibration generating mechanism that agitates the adhesive in an effort to encourage flow of adhesive particulate towards the pump inlets while also assisting with drawing the addition gas or “make-up” gas through the stacked adhesive particulate. This vibration generating mechanism is mounted on a near-vertical surface along a side of the tote including the pump inlet in conventional systems. Although this positioning of the vibration generating mechanism provides sufficient vibration of the adhesive particulate located in close proximity to the back side of the tote, the vibration energy dissipates and becomes less effective as it moves through the mass of adhesive particulate. Consequently, the effectiveness of vibration to break apart or loosen adhesive that is stuck together (such as by being coalesced) in clumps far away from the vibrating surface is reduced. These clumps of adhesive particulate may pass through this zone of insufficient vibration and may then lead to blockages at the pump inlet.
Furthermore, the pump inlet of conventional tote-based systems is generally positioned above the lowest point in the adhesive bin. As a result of this arrangement, the adhesive particulate below the pump inlet is effectively trapped and the pneumatic pump is incapable of removing it from the adhesive bin. Over time, this adhesive particulate will solidify into a solid mass that could break off into clumps that may lead to blockages at the pump inlet. Because of the difficulty in drawing “make-up” air to the pump inlet as described above, it has been impossible to move the pump inlet downwardly further without exacerbating the problems with the pneumatic pump becoming starved for air flow. In addition, the storage capacity of the adhesive bin cannot reasonably be reduced without requiring refills too frequently for convenience of end users. Thus, the conventional tote-based systems continue to struggle with problems caused by clumping of adhesive particulate and air flow to the pump inlets.
There is a need, therefore, for improvements in hot melt adhesive systems, and specifically, a need for an adhesive storage unit and method for use with a transfer pump that addresses present challenges and characteristics such as those discussed above, particularly tailored for use in transferring adhesive particulate from bulk supply to melter(s).